1. Field of the Invention
The present invention relates to a hybrid integrated circuit device with a built-in microcomputer and, in particular, to a hybrid integrated circuit device provided with a non-volatile memory which feeds data to the microcomputer, and which can be treated as an electronic part which functions independently.
2. Description of the Background Art
An EPROM element with an ultraviolet light irradiation window provided in its surface by which it is possible to erase stored data written on a chip by ultraviolet irradiation and rewrite into that memory is preferably used in various types of electronic devices. These EPROM elements are usually mounted on a printed board provided that they can detachably be mounted for subsequent rewriting. Most of these EPROM are mounted together with a control- or drive-integrated circuit on a printed board.
For electronic devices which must be small and light-weight, a technique known as "chip-on-board" is adopted, wherein a semiconductor integrated circuit (IC) chip is directly mounted on a printed board, and after the required wiring is implemented, the IC chip and the wiring section are covered with a synthetic resin. However, in an electronic device for which an EPROM element is required, because it must be possible to erase the stored data by directing ultraviolet light onto the EPROM element, and to rewrite into the element, the chip-on-board technique whereby an EPROM chip is mounted directly on a printed board and covered with a synthetic resin cannot be adopted. For this reason, in an electronic device for which an EPROM element is required, there is no other choice but to use an EPROM element incorporated in a SADIP-type package. The development of an small-size, light-weight unit is hence hindered.
FIG. 1 is a perspective drawing of an EPROM substrate, which explains the mounting structure of a conventional EPROM element. One part of an EPROM element 44 is shown in section.
A plurality of through-hole terminals 43 and a plurality of male connector terminals 55 made of conductive material are formed on the main surface of an insulating substrate 42 made from glass-epoxy resin or other similar material. In addition, a conductive wire pattern 41 is also formed, mutually connected to the through-hole terminals 43 and the male connector terminals 55. An external conductive lead 48 of the EPROM element 44 incorporated into a SADIP-type package is inserted through the through-hole terminal 43 and electrically connected by soldering to the through-hole terminal 43. In addition, the external conductive lead 48 is mechanically secured to the insulated substrate 42.
The EPROM element 44 is provided with a ceramic header 45 and a ceramic cap 46. The external conductive lead 48 is bonded to the header 45 using a glass material with a low melting point. An element mounting section 50 which is produced from a sintered gold paste made up of a large quantity of gold powder mixed with glass is also bonded directly to the header 45, or indirectly to the header through the low melting point glass material which is extended to the element mounting section 50. An EPROM chip 51 with an ultraviolet emitting surface on the top is mounted on the element mounting section 50. An electrode of the chip 51 is connected to the external conductive lead 48 with a fine metal wire 52. The cap 46 is a cover member provided with a window 53 vis-a-vis the ultraviolet emitting surface of the EPROM chip 51. The cap 46 is bonded to the header 45 using a low melting point glass, and it seals the EPROM chip 51 which is positioned on the header 45. The EPROM substrate having the above structure is formed independently of the main circuit print board. The EPROM element 44 is connected to a microcomputer or the like mounted on the main circuit print board. This connection is made through the external conductive lead 48, the through hole terminal 43, the conductive wire pattern 41, a male connector terminal section 55, and a female connector (omitted from the drawings).
The external form of a package when such a conventional EPROM element mounting method is used is extremely large in comparison with the EPROM chip 51. In addition to occupying a large area in plan view, the height of the elements is also several times the height of the chip, which is a severe handicap in providing a thin-type printed board. After the external conductive lead 48 is inserted into the through hole terminal 43, the EPROM element must be secured by solder or the like. In addition, a particularly troublesome drawback is the fact that, before mounting on the insulated substrate, the EPROM element must once be assembled in the package. Because the EPROM element is provided with an ultraviolet emitting window, the package is assembled in a SADIP-type package made from a ceramic and, because this package is sealed in low melting point glass, a high temperature (400.degree. C. to 500.degree. C.) sealing process is adopted. If the electrode (aluminium) of the EPROM chip and the fine metal wire which connects the electrodes (aluminum) of the EPROM chip to the external conductive lead are not made from the same type of material, an alloy is produced at the sealed section during the high temperature sealing process and the resistance of the wire increases. This can cause the wire to break. A fine aluminum wire is usually used to avoid this kind of trouble, but, in this EPROM chip, the earth electrode of the EPROM chip is wired to the mounting section of the chip which is formed with gold paste, because the substrate of the EPROM chip must bear earth potential. Here as well, there is a tendency for a binary or multiple alloy reaction to occur between the gold in the gold paste and/or the metal in the metal foil or the like, and the aluminum. For the above reason, a small silicon leaf covered with aluminum on the head referred to as a gland die, is attached to the chip mounting section formed from the gold paste, and the earth electrode of the EPROM is connected to the top of the gland die. The conventional mounting structure has many drawbacks accompanied by the above complicated process. Thus, the conventional mounting structure does not satisfy any of the requirements for small size, light weight, and low cost.
The EPROM mounting structure shown in FIG. 2 has been proposed to eliminate this type of problem. This mounting structure will now be explained with reference to the drawing.
An insulated substrate 60 made from a glass-epoxy resin or other similar material has a main surface 60a on which is formed a wiring pattern 60b. A chip mounting area 60c which supports an EPROM chip 61 is provided on the insulated substrate 60. The wiring pattern 60b is routed on the main surface 60a from a point close to the area 60c and is connected to a male connector terminal (omitted from the drawing). The EPROM chip 61 is mounted on the area 60c. A surface electrode of the chip 61 is connected to the wiring pattern 60b by a fine metal wire 62. The substrate of the EPROM chip 61 as well is connected to the mounted wiring pattern 60b by one strand of the fine metal wire 62. An ultraviolet transmitting window material 64 of the EPROM chip 61 is fixed on the ultraviolet-emitting surface 61a of the EPROM chip 61 through an ultraviolet transmitting resin 63 [for example, TX-978 (trademark), manufactured by Toray].
The window material 64 is made from a commonly known ultraviolet transmitting material such as quartz, transparent alumina, or the like. The top surface 64a of the window material 64 is a surface which introduces light to the ultraviolet-emitting surface 61a of the EPROM chip 61. The parts of the window material 64 other than the top surface 64a, the fine metal wire 62, and the part connecting the fine metal wire 62 with the wiring pattern 60b are covered with a synthetic resin 65 [for example, MP-10 (trademark), manufactured by Nitto Denko Corp.]. If the base of the chip mounting area 60c of the substrate 60 is situated on a concave at about half the height of the substrate 60, it is possible to further reduce the combined thickness of the insulated substrate 60, the EPROM chip 61, and the window material 64, while formation of a floodgate by the synthetic resin 65 effectively prevents moisture from entering. The EPROM mounting structures shown in FIG. 1 and FIG. 2 are disclosed in Japanese Patent Laid-open No. 83393/1985 (HO5K 1/18 ).
Because the EPROM chip is die-bonded to the printed board in the EPROM mounting structure shown in FIG. 2, the printed board is reduced in size by only the amount of reduction of the EPROM. However, although it is not shown in FIG. 2, because the microcomputer which is to be fixed near the EPROM chip and its peripheral circuit elements are fabricated as discrete electronic parts, the problem remains that most of the size reduction is not achieved, if the printed board on which the EPROM is mounted is viewed as a system. In addition, in the EPROM having the structure illustrated in FIG. 2, rewriting of program data onto the EPROM chip must be performed after the program data has been erased by exposing the printed board to ultraviolet light, and by touching a write-in terminal, such as a probe or the like, to the conductive pattern extending from the EPROM chip. For this reason, usual conventional ROM writers cannot be used. This entails a problem of troublesome in rewriting onto an EPROM.
Also, with the EPROM mounting structure shown in FIG. 1, the EPROM can detachably be mounted on the main printed board, so that a usual ROM writer can be used for writing. However, in the same manner as with the mounting structure shown in FIG. 2, the circuits around the EPROM, specifically, the microcomputer and its peripheral circuit elements, such as LSIs, ICs, and the like, are constructed as discreet electronic parts in the same manner as in FIG. 2. This causes the printed board as well as the total system to be large in size, making it impossible to provide a small and light integrated circuit as the user requires. This is a major problem. In addition, an independent printed board for the EPROM element is required, and the wiring pattern 41 for connecting the EPROM element 44 to a microcomputer becomes very long, bringing about the problem that size reduction cannot be achieved.
With the EPROM mounting structures shown in FIG. 1 and FIG. 2, the complete system becomes large, as outlined above. In addition, because the conductive pattern which connects the EPROM and the peripheral circuit elements are exposed, reliability is lowered.
Furthermore, with the EPROM mounting structures shown in FIG. 1 and FIG. 2, because the EPROM and its peripheral microcomputer and circuit elements, such as LSIs, ICs, and the like are exposed, irregularities are formed on the upper surface of the substrate, reducing operability and making servicing difficult.